目前用的cin，肯定会TLE，但是小数据不知为何WA了。

#include<iostream>
using namespace std;
long long n, m, S, ans, lastans, root, head[5000005], tot, siz[5000005], id[5000005], seg[50000005], top[5000005], fa[5000005], son[5000005], cnt, deep[5000005];
inline unsigned int get(unsigned int x)
{
	x ^= x << 13;
	x ^= x >> 17;
	x ^= x << 5;
	return S = x;
}
struct node
{
	int y, nex;
}s[5000005];
void add(int i, int j)
{
	s[++tot].y = j, s[tot].nex = head[i];
	head[i] = tot;
}
void dfs1(int now, int father)
{
	int nowson = -1;
	fa[now] = father;
	siz[now] = 1;
	deep[now] = deep[father] + 1;
	for (int i = head[now]; i; i = s[i].nex)
	{
		int y = s[i].y;
		if (y == father)
			continue;
		dfs1(y, now);
		siz[now] += siz[y];
		if (siz[y] > nowson)
			nowson = siz[y], son[now] = y;
	}
}
void dfs2(int now, int topf)
{
	top[now] = topf;
	id[now] = ++cnt;
	seg[cnt] = now;
	if (!son[now])
		return;
	dfs2(son[now], topf);
	for (int i = head[now]; i; i = s[i].nex)
	{
		int y = s[i].y;
		if (y == fa[now] || y == son[now])
			return;
		dfs2(y, y);
	}
}
int query(int now, int k)
{
	while (k >= id[now] - id[top[now]] + 1 && now != root)
	{
		k -= (id[now] - id[top[now]] + 1);
		now = fa[top[now]];
	}
	return seg[id[now] - k];
}
int main()
{
	cin >> n >> m >> S;
	for (int i = 1; i <= n; i++)
	{
		int u;
		cin >> u;
		if (!u)
			root = i;
		else
			add(u, i);
	}
	dfs1(root, 0);
	dfs2(root, root);
	for (int i = 1; i <= m; i++)
	{
		long long u = (get(S) ^ lastans) % n + 1, k = (get(S) ^ lastans) % deep[u];
		lastans = query(u, k);
		ans ^= 1ll * i * lastans;
	}
	cout << ans;
	return 0;
}